PROJECT SUMMARY Advances in genomics and epigenetics have improved our understanding of the genetic regulatory landscapes underlying many types of cancer. Within a specific type of cancer, there are several distinct genetic subtypes depending on the underlying mutations. Our research has identified Arid5b as a gene that interacts within a transcriptional network that regulates hematopoiesis. Polymorphisms in Arid5b are associated with an increased risk of developing pediatric leukemia and with an increased risk of treatment failure. Yet the role of Arid5b in normal hematopoiesis and the mechanisms underlying how alterations of Arid5b contribute to leukemogenesis are unknown. Work in other cell types suggests that Arid5b regulates development in part by directing epigenetic complexes to genomic loci to influence gene expression. It is now recognized that epigenetic regulation (DNA methylation, histone modifications, nucleosome remodeling, etc?) is disrupted in leukemia and many other cancers. However, an understanding of how epigenetic dysregulation contributes to the activation of oncogenic programs is limited. We propose that Arid5b plays a central role in a transcriptional network that regulates normal hematopoiesis. Arid5b functions in part to facilitate proper genomic targeting of epigenetic complexes to regulate gene expression. Alterations in Arid5b disrupt this network and contribute to leukemogenesis. We will study primary murine hematopoietic stem and progenitor cells, human leukemia cell lines, mouse models of leukemia and primary patient leukemia samples to describe the role of Arid5b in normal and malignant hematopoiesis. We will use a complementary suite of molecular biologic approaches to define a comprehensive Arid5b interactome in hematopoiesis and leukemia. Transcriptome analysis will describe a global gene expression profile influenced by Arid5b. ChIP-seq will identify direct Arid5b target genes within its transcriptional network. Analysis of epigenetic marks at promoters of Arid5b target genes will describe the epigenetic profile directed by Arid5b. Lastly, utilizing BioID we will identify novel Arid5b-protein interactions and complexes through which Arid5b regulates gene expression. Collectively our work will contribute towards improving our understanding of the complex mechanisms underlying transcriptional regulation in normal hematopoiesis and how dysregulation of these networks contributes to leukemogenesis.